A novel telephone station signaling lock circuit was disclosed in U.S. Pat. No. 4,453,042 entitled "Telephone Station Signaling Lock Circuit" which issued on June 5, 1984 to A. L. Wolf and J. G. Wagoner. As disclosed in that patent, the signaling circuit was locked or disabled by a microprocessor in response to operation of a station lock pushbutton To unlock or enable the signaling circuit, the station lock pushbutton was again operated and selected keypad pushbuttons were subsequently operated. If the character signals provided by operation of these keypad pushbuttons are identical to a predetermined unlock code, the microprocessor then unlocks the telephone station. However, if the unlock code is not known, the signaling circuit of a locked telephone station can not be unlocked, even in cases of emergency.
The previously referenced copending application for a Master Unlock Circuit overcomes the limitation through a novel arrangement for a master unlock code. However, that arrangement still requires use of a station lock pushbutton. The present invention discloses a novel arrangement for restricting the telephone station to local call without the requirement of a station lock pushbutton.